Method of producing ceramic gauges



Oct. 10, 1950 R. TWELLS I 2,525,324

METHOD OF PRODUCING CERAMIC GAUGES Original Filed Nov. 26, 1943 CERANHC MATERIALS WFJGHING & MIXING LIQUID CARRIER BALL MILLING I PUG-SING & I EXTRUSION FORMING i DRYING FORMED BLANKS SHALING Fig 2 BLANKS TO OVERSIZE KILN FIRING DIAMOND GRINDING TO FINAL 2O /5 DIMENSION I I i ifiiiiijji -f 3 INVENTOR ROBERT Tw EL LS Patented Oct. 10, 1950 UNITED STATES PATENT OFFICE METHOD OF PRODUCING CERAMIC GAUGES Robert Twells, Fostoria, Ohio Original application November 26, 1943, Serial No.

511,768. Divided and this application November 27, 1945, Serial No. 631,118

ticularly to the method of making the same. This application is a division of my co-pending application for United States Letters Patent, filed November 26, 1943, Serial No. 511,768, which issued into Patent No. 2,495,789 on January 31, 1950.

The gauges in the prior art have long been made from tool steel or the like which has been heat-treated to obtain maximum hardness, but these gauges suifer the disadvantage of being unduly subject to wear by abrasion by the objects Whose dimensions are being tested. This wear materially changes the dimensions of the gauge within a relatively short period of use so that its size falls outside of the narrow limits of variation allowed in dimensions of gauges. After the worn gauge had changed its dimension to fall outside of the allowed tolerance, the gauge was often repaired by coating the tool steel with a hard abrasive-resistant material, such as chromium, preferably by a plating process, which allowed the further continued use of the gauge for a considerable length of time. However, the durability or wearing characteristics of such gauges in use, either plated or unplated, still left much to be desired.

Glass has also been used in gauges, but the brittleness of the material caused frequent breakage and chipping so as to destroy the usefulness of the gauge. It also has been suggested to use hard refractory bodies which are found in nature; such as feldspar, quartz, zircon, beryl, .topaz and others from which the gauges were laboriously formed by cutting away a body of the material to the desired conformation of the gauge having the required dimensions. These applications, however, have not found wide application in industry.

The present invention provides a gauge which is made of tough, exceedingly hard material which is wear-resistant and will allow a number of passes in use which is many times greater than the gauges presentlyavailable. This is not only an advantage from the production angle, in that the required dimensions of the measured objects are more closely maintained, but also it is cheaper from the cost angle inasmuch as replacement is not necessary as frequently as With gauges presently in use. I

tion when the material is easily cut and formed, and given its final cutting to exact'dimensions after firing whenit is in vitrified-condition while the material'is tough and exceedingly hard. When The gauge contemplated is given: its general form in its prefired, unvitrified condi- 2 the gauge is given its general form with the material thereof in unfired condition, an allowance must be made for shrinkage taking place during firing which is preferably carefully predetermined so that the dimensions of the fired body of the gauge closely approaches its final dimension with;

a smalloversize to allow some leeway for a final grinding operation cutting the gauge to exact size. Yet the oversize must be relatively small to reduce final grinding to a minimum to obviate the necessity of removing large amounts of the exceedingly hard vitrified material formed by the burning or firing.

It is, therefore, a principal object of this invention to provide a gauge made of artificiallybonded ceramic material which has great harda ness and durability.

It is a further object of this invention to provide a gauge which consists largely of non-plastic metallic oxides, of the type which whenmixed with a liquid carrier are not auto-ce'mentitive to produce a body of suitable plasticity t0 be ex.-

truded or capable of retaining predetermined configurations, artificially-bonded together by. a

1 small percentage of ceramic flux.

It is a further object of this invention to provide a method of making gauges wherein nonplastic metallic oxides are artificially-bonded together by a small percentage of ceramic flux which will result in a gauge having a body which is extremely hard and tough so as to be wearresistant and durable.

Other objects and advantages of this invention relating to the arrangement, operation and function of the related elements of the structure, to various details of construction, to combinations of parts and to economies of manufacture, will be apparent to those skilled in the art upon consid-..

eration of the following description and appended claims, reference being had to the accompanying drawings forming a part of this specificatiorr wherein like reference characters. designate corresponding parts in the several views.

In the drawings:

Fig. 1 is an elevational view of a plug gaugeprovided with guide surfaces made in accordance with this invention. Fig. 2 is a diagrammatic scheme, showing the different steps in the method of making ceramic gauges.

Fig. 3 shows a plug type gauge'as inserted in a handle ready for use.

Referring to Fig. 1, a plug type gauge. is shown? having a tang H] of tapering contour adapted to attach the gauge to a holder or handle as will be discussed hereinafter. Forward of the tank ID a head I I is provided which is substantially larger than the tang and forms a stop for a gauge surface l2 positioned forwardly of the head H. A guide surface 13 is positioned forwardly of the gauging surface i2 and serves to align the gauge surface with the aperture whose dimension is to be measured so as to prevent chipping by impact of the gauge surface with the perimeter of the aperture. The guide surface l3 also prevents the gauge from j oggling in the aperture which would tend to cramp the gauge therein so as to cause undue wear on the gauge surface, the guide surface tends to maintain alignment between the gauge and the aperture. Centering apertures l4 are provided in each end of the plug gauge, being formed therein during the prefired forming stage of the gauge in the process of makng the same as will be described further hereinafter.

The use to which a gauge of this type is put makes it highly advantageous that the body thereof shall be made of a material which has maximum hardness so as to prevent wear when it is' being used in gauging operations and also that it shall be tough as contradistinguished from brittle to prevent chipping under the impact of blows such as might arise in careless handling of the gauge or dropping thereof on a hard-surfaced floor. This invention provides a gauge which fulfills these desirable characteristics and at the same time has the added advantage that during a stage in the fabrication of the gauge this hard tough material is relatively soft and easily formed by working to a desired contour to reduce the cost of making the gauge to a feasible figure. The process of making a typical gauge will now be described in detail. I

The basic material of which the gauge is made consists primarily of a metallic oxide, or a mixture of several oxides having, in general, very high temperatures effusion, such as for example, aluminum oxide which is the preferred material. As is well known, aluminum oxide is non-- plastic and taken alone is not readily formed into cohesive bodies which may be shaped into the desired contour of the gauge to allow firing. Furthermore, aluminum oxide taken alone, has such an extremely hightemperature of fusion that it is impracticable to make the gauge by the process of fusing it into a homogeneous body. Sintering aluminum oxide into a cohesive body requires a much lower temperature than to completely fuse the same, but still requires a temperature which is too high for convenient commercial'utilization. It has been found that when ceramic fluxes are added to the aluminum oxide to form a cementing substance to fill the inter: stices between the particles or granules of aluminum oxide to form a homogeneous body, the resulting body partakes largely of the physical characteristics of the aluminum oxide, such as for example great hardness, and also suificient toughness to be infrangible.

The addin of the ceramic fluxes, such as for example oxides of the metals found in groups I, II and IV of the periodic table of elements, especially the alkaline earth group, has the further advantage of reducing the firing temperature at which vitrification of the ceramic body occurs. In these groups Na, K, Be, Mg, Ca, Ba, Si, Zr, and Ti, are the preferred oxides, the remaining oxides are usually very expensive or too rare for practical use. Mixtures of this type may vary widely intheirconstituents. For example, if aluminum oxide is to be the basic substance, its percentage of the whole may vary from to substantially pure aluminum oxide, while the remainder consists of the ceramic fluxes discussed hereinabove and/or mineral and organic plasticizers and binders. However, as the percentage of aluminum oxide increases, the vitrification temperature also increases so that there must be a balancing of factors to obtain the desired characteristics of hardness and toughness in the finished product as against the vitrification temperature used in the kiln in which the bodies of the gauges are fired. The characteristics of hardness and toughness of the aluminum oxide are not substantially decreased by the addiiton of ceramic fluxes up to 20% of the whole, however, there is a point reached at which the bodies formed by these admixtures are substantially influenced by the addition of the ceramic fluxes which, in general, do not contribute many desirable characteristics to the completed vitrified body. It is desirable to maintain the percentage of the fluxes as low as possible commensurate with the reduction. of the vitrification temperature used durin the firing stage.

For aid in forming, it is sometimes desirable to add a mineral binder which has a characteristic of plasticizing the admixture, such as clays of certain types, so that it is in a proper condition to form a cohesive body which is capable of being worked and handled in the various steps in the process of making the gauge body. The mineral binder usually acts also as a ceramic flux at the high firing temperatures used to vitrify these bodies. To avoid over-dilution of the properties of the pure oxides, organic binders may be added to give a cohesive quality to the elements of theadmixture to hold the body temporarily together during the different steps inthe process of manufacture. The organic binder will not affect. the composition of the completed body of the gauge, bein'gremoved during the fir-.. ing process thereof, due to the fact that. the temperature is sufficientlyhigh to burn out completely the organic substances, which are used. No trace will be found of to form the binder. them in the completed body of the gauge as it. is removed from the kiln.

Turning now to Figure 2 of thedrawings, a diagrammatic scheme is illustrated showing the various steps taken in the fabrication of thegauge. Beginning with the raw material, which. may be anon-plastic metallic oxide (or a combination of such oxides) such as aluminum ox ide, and a ceramic .fiux which may include an.

oxide of alkaline earth metal, such as magnesium oxide, these materials are carefully weighed to obtain a proper proportion between the constit uents of a batch. These raw materials may be calcined and finely divided or pulverized" by grinding prior to their being mixed together, or, in the event that these materials are not sufficiently finely divided to serve, the mixture may be placed in a ball mill and provided with a liquid carrier to facilitate the further pulverization ,of these raw materials to the degree desired.

When the grinding process in the mill is completed, the slip formed therein is withdrawn from the mill and placed in a storage tank. The liquid carrier, which may conveniently be water or any other substance which has the proper char.- acteristics for use in the grinding mill, is partially removed, usually byfilter pressing, and the cake so formed is placedv in a pugging machine and again thoroughly mixed to form a uniform'mixture of the constituents of thebatch. After the;

pugging has served its purpose, the ceramic batch is extruded and formed into blanks having the size and shape to allow forming of a prefired gauge body.

These blanks are then allowed to dry to bonedryness which removes a large percentage of the moisture and gives the blank a consistency similar to chalk, which is a suitable condition for shaping the blank into substantially the final conformation of the completed gauge, with an allowance, however, being made, firstly for the shrinkage which the gauge body undergoes during the vitrification thereof in a kiln, and secondly to obtain a margin of extra material on the vitrified body which may be removed in the final grinding of the gauge. These oversized unfired gauge bodies are then placed in a kiln and fired at a temperature preferably over 'l600 centigrade until vitrification of the body takes place and an extremely hard, dense, tough gauge body is formed, slightly oversize to allow final grinding to size. The hardness of the vitrified body or gauge-measurin part is preferably of a hardness of over Mohs scale 8 and consists predominantly of exposed ground crystals or granules of non-plastic or metallic oxides.

Due to the fact that commercially obtainable ceramic materials vary widely in their purity and that slight changes in the percentages of the constitutents of such impurities affect changes in the characteristics of the mixture and thereby of the final ceramic gauge of the invention, certain characteristics of the final product cannot be forecast with absolute accuracy. However,

the characteristic of hardness and toughness can a be forecast with reasonable accuracy but shrinkage characteristics of the bodies having different constituents vary too Widely to be forecast within the desired limits and must be determined by actual experimentation with the ceramic mixture to be used for the gauges. The shrinkage characteristics also vary due to diiferent densities in the unfired blanks, which may arise from variations in moisture content, extruding pressures and the like. Once determined, these shrinkage characteristics are sufficiently constant, depending upon the uniformity of the percentage of the constituents and density, that the oversize of the unfired blanks to compensate for shrinkage may be held to limits whereby an oversize of 0.01 to 0.02 inch may be obtained in the fired blank to give a reasonable amount of extra material available for the final grinding step.

Thereafter the gauge is ground to final dimension, preferably by a diamond grinding process as is well known in the art; For this purpose the centers M, as shown in the completed gauge in Fig. 1, may be used. These centers are first formed in the blank during the chalk stage of the ceramic material at which time they maybe readily cut into the end faces of the blank and establish the center line of the gauge which remains so even after vitrification has taken place.

The gauge body is then mounted in a handle l (Fig. 3) having a, central longitudinal aperture I6 provided with outwardly tapering portions adjacent the ends of the handle [5 which form seats for the tangs ll! of the gauge elements. Two of these gauge elements are used in connection with the handle l5, one element ll being a Go gauge and a second element 18 being a No-Go gauge, each having a predetermined relative size. In order to remove the gau e e ements I! and I 8 conveniently from the handle [5,

a transverse aperture l 9 is provided adjacent the end face 20 of the tang ll) of the gauge element I! which facilitates the removal of the gauge element from the aperture l6. Thereafter the gauge element I8 is readily removed by inserting a member (not shown) into the aperture IE to drive out the tang of the gauge portion l8.

In the above discussion it has been assumed that the ceramic fluxes or clay used in connection with the batch described have a plasticizing characteristic which would allow the formation of a cohesive body without the use of any temporary binder. However, if a batch does not have the plastic characteristic, an organic binder may be added to the batch to serve the purpose of temporarily holding the constituents of the batch together to form a cohesive body. Such an organic binder may be gum tragacanth, dextrine, resins, or any other substance well known in the art. This material may be added directly to the grinding mill with the liquid carrier, or it may be added at any other convenient stage during the process of making the gauge.

A specific example of a ceramic batch from I which a gauge may be made is this preferred composition which consists of Per cent Alumina Clay 10" The clay is mineral plasticizer in the formative stage of the gauge and is the fiux which in part forms a glassy matrix holding the alumina artificially together after vitrification of the body firing, may be made by other methods. For example, the slip which comes from the grinding mill may be used for casting into a porous mold to form the body of the gauge. This is accomplishedrby pouring the slip directly into the porous mold after its removal from the grinding mill, the mold being of such a nature that it absorbs from the slip the liquid carrier, leaving the fines cast into the form of the mold. The1-e-' after the casting with or without the surrounding mold is subjected to a drying atmosphere with or without the applicationv of heat so as to remove a large percentage of the moisture from the mold and/or casting. The casting, which is chalky in nature, is then further shaped by grinding to its oversize conformation necessary prior to firing. The firing and final grinding processes thereafter are substantially the same as that described above.

Another method by wh ch these gauge bodies may be prepared for firing is to mix finely divided metallic oxides, such as aluminum oxide, thoroughly with finely-divided ceramic fluxes, while both are in a dry state and combining the miX- ture uniformly with an organic binder such as dextrine or wax, also being in dry or nearly dry condition. This mixture of finely divided mate- C. The

rials 'isth'en compressed indry ornearly dry con-:- a

dition in a flexible rubber mold, or by any other mold device which allows uniformapplicationisof pressure --to thedry powders, until a self -sustainingbody is for-med which will be substantially. in a chalk condition, having a small percentage .of moisture included' The mold may in general have a shape, having a rough approximation 'ofthe unfired' oversize gauge body, the blankbeing.

thereafter further shaped: by the same process describedabove=with the other methods disclosed.

Another alternate process is to place-the raw materials into a ball mill and grind them to fineness without the'use'of a liquid medium; The

truding of the blank, an organic binder'such-asartificial resins 'can'be employed. The blank is then formed by hot-pressing the -material such as in molding, synthetic resins formed by-th'e condensation of phenols and formaldehyde. The firing and the final diamond grinding'of these bodies are substantially the same as before.

It -is*t0'be understood that the above detailed description of thepresent invention is intended to'disclose an embodiment thereof to those skilled in the art, but that the invention is not to be construed as limited in its application to the details of construction and arrangement of parts illustrated in the.accompanying drawings, since the inventioniis capable of being practiced and carried out in'various. ways without departing from the spirit'of the invention. The language used in the specification relating to the operation and function of the elements of the invention is employed for purposes of" description and not of limitation,fland it is not intended to limit the scope of thefollowing claims beyond the requirements of the prior art.

What is claimed:

1.. The method of making a synthetic ceramic gauge comprising binding together into a bank a mixture of finely divided particles of aluminum oxide having. a high temperature of fusion and a hardness over Mohs scale 8 with small amounts of finely divided ceramic fluxes, shaping the blank to a predetermined contour and oversize to allow for shrinkage during firing and a small amount of extra material, firing the shaped blank at a temperature of at least 1500 C. but below the temperature of the fusion of the aluminum oxide producing thereby, a body comprising particles of aluminum oXide bonded togetherxby a glassy matrix, and removing by grinding the extra ma terial to form a gauge having a gauging surface of a predetermined final size consisting predominantly of particles of aluminum oxide.

2. The method of making a synethetic ceramic gauge comprising mixing finely divided particles of alumina having a high temperature of fusion and a hardness over Mohs scale 3 with a small percentage by weight of finely divided ceramic fluxes, adding a binder to said mixture to form a cohesive ceramic batch, shaping the batch into a blank having a predetermined contour and oversize to compensate for shrinkage during firing and a smallamount of extra material, firing the shaped blank at a temperature of at least s 1500 C. but below thetemperatureof fusionziof the alumina to produce thereby a body-comprising particles of alumina'bonded togetheraby a glassy matrix, and removing by abrasion the extra material to form a gauge having-a measuring surface of predetermined final size consist; ing predominantly of finely divided particles of alumina.

3. The method of making a gauge comprising;- binding together'into'ablank a mixtureoffinely; divided metallic oxides selected fort thein temperatures of fusion and a'hardnessover Mohfs; scale 8 with small. amounts. of finely divided: ceramic fluxes, forming the-:.b1ank..to predeteremined oversize to allow for shrinkage during: firing and :a small amount'of extra: material for: grinding, firing the formed blank iatq'a tempera-e ture of at least 1500 C. but below'the temperaeture of fusioniof 'the .oxides,xyand removinggther. extra material. by'grinding to form a; gauging: surface of particlesoftmetallic oxide-.zbonded -to: gether by a glassy matrix;

4. The method of making a plugsgauge comprising forming an unfired bodyof a largevpercentage' of finely, divided metalliooxide havinga-w high temperature of :fusionanda hardness .over. Mohs scale 8, and a smallzpercentagevof finely divided ceramic flux, providing theun-fired'body; with centers along an axis of the -body',co-ntouring the unfired body a predetermined oversize to: compensate for shrinkage during firing, firing; the body at a temperatureover 1500 C. but be low the fusion temperature of the-:oxide to vitrify the body into an abrasion-resistant,-.hard-tough body consisting of the particles of the-metallic. oxide held in a glassy matrix andrgrinding thebody to predetermined size'aboutsaid centers.

5.- The method of making a gaugefrom finely. divided metallic oxide:particles-having a hardness over Mohs scale :8 'andr'high temperatures of fusion, comprising forming-.;a,- body of-: the-.- oxide particles cemented together byhaving theinterstices filled with a glassy material andgrinding the body to desireddi-mension whereby.- a gauging surface is formed consisting substan tially of ground particles of the-metallic oxide.

ROBERT TWELLS.v

REFERENCES. CITED The following. references are-of record inithes file of this patent:

UNITED STATES PATENTS OTHER REFERENoEs- Grits and Grinds, C. S. Reasby, page 1' (glass plug gauges) May 1943, No. 5, Vol. 34, published by Norton 00., Worcester, Mass, class 51, subclass 283. 

1. THE METHOD OF MAKING A SYNTHETIC CERAMIC GAUGE COMPRISING BINDING TOGETHER INTO A BLANK A MIXTURE OF FINELY DIVIDED PARTICLES OF ALUMINUM OXIDE HAVING A HIGH TEMPERATURE OF FUSION AND A HARDNESS OVER MOH''S SCALE 8 WITH SMALL AMOUNTS OF FINELY DIVIDED CERAMIC FLUXES, SHAPING THE BLANK TO A PREDETERMINED COUNTOUR AND OVERSIZE TO ALLOW FOR SHRINKAGE DURING FIRING AND A SMALL AMOUNT OF EXTRA MATERIAL, FIRING THE SHAPED BLANK AT A TEMPERATURE OF AT LEAST 1500*C. BUT BELOW THE TEMPERATURE OF THE FUSION OF THE ALUMINUM OXIDE PRODUCING THEREBY A BODY COMPRISING PARTICLES OF ALUMINUM OXIDE BONDED TOGETHER BY A GLASSY MATRIX, AND REMOVING BY GRINDING THE EXTRA MATERIAL TO FORM A GAUGE HAVING A GAUGING SURFACE OF A PREDETERMINED FINAL SIZE CONSISTING PREDOMINANTLY OF PARTICLES OF ALUMINUM OXIDE. 